Chondromas And Their Impact On Bone Health

Introduction

Bone health is very important, particularly during development, for mobility, protection of vital organs, providing space for bone marrow, and storage and supply of calcium. There are many pathological conditions that can alter the health and subsequently the structure of our bones.

Chondromas are rare, benign tumours of the hyaline cartilage, the soft, cushion-like tissue at the ends of bones where they meet to form joints.¹ They are often found in the humerus (upper-arm bone), tibia (lower leg bone), and femur (thigh bone) as well as short bones in hands and feet. They are composed of only cartilage cells, namely chondrocytes, and matrix. Normally, they are isolated and have a slow, monotonous growth pattern.² Though the cause for chondromas is not known, they are thought to occur due to either overgrowth of cartilage or continuing growth of the embryonic cartilage. Unfortunately, chondromas can occasionally inhibit bone growth in the affected area and potentially lead to skeletal deformities, or bone fractures. In some cases, chondromas can undergo malignant transformation into chondrosarcoma.

Types of chondromas

Chondromas can be classified as:

• Enchondromas originate from the hollow section of the bone called medullary cavity.
• Periosteal chondromas originate from the dense outer layer of bone called the cortex.
• Soft tissue chondromas (STCs), originate in soft tissues and not bones.

Enchondromas

In humans, mature bones are formed when the tissue at the ends of long bones, called the growth plate, closes after puberty (between ages 16-18), halting the growth and development of long bones.³ Enchondromas are likely to develop due to mutation and the subsequent overactivation of the receptor that delays terminal-stage differentiation of proliferating chondrocytes.⁴ In patients with Maffucci syndrome and Ollier syndrome, both of which are characterised by multiple enchondromas, the malignant transformation of enchondroma into chondrosarcoma is as high as 50%.⁵ Epidemiologically, enchondroma is the 2^nd most common benign cartilage lesion affecting 3% of the population, with the most common regions being the hands (60% of all cases) and femur (accounting for 20% of all cases).⁶ 

Periosteal and soft tissue chondromas

Whilst sharing some basic pathological features as enchondromas, periosteal chondromas and soft tissue chondromas are rare benign chondromas present in different regions. Periosteal chondromas occur on the periosteal surface of long and short tubular bones. STCs commonly occur in soft tissues on the hands and feet, often with no relation to the underlying bone, either tendon or tendon sheaths.⁷ They do not invade surrounding bone. Usually, STCs are round, slow-growing masses made of hyaline cartilage, rarely exceeding 3cm in diameter.⁸ Only 1.5% of all chondroma cases worldwide are associated with STCs, with most cases (over 95%) occurring in the hands and feet, commonly between the ages of 30-60.^9,10 STCs are commonly painless unless they exert pressure onto weight-bearing surface or surrounding structures. So far, no cases of STC malignant transformation have been reported.^8,9 Periosteal chondromas account for 2% of all chondroma cases worldwide, occurring mostly in people assigned male at birth below the age of 30.^11,12,13 They are slow-growing tumours (smaller than 3cm) commonly present in the humerus, femur and tibia.^12,14 A tissue diameter beyond 3cm is associated with periosteal chondrosarcoma, which would continue growing even after bone maturity.¹⁵ Patients with periosteal chondroma present signs of swelling and aching pain, whilst some can feel the tumour mass.

Impact of chondromas on bone health

Chondromas have differing impacts on bone health depending on their location and size. 

Localised effects on bone

Skeletal abnormalities, unequal limb lengths, and a possible risk of developing chondrosarcoma are just a few of the clinical issues brought on by enchondromas. As previously mentioned, there are 2 clinical disorders associated with the presence of multiple enchondromas, namely Ollier and Maffucci disease, both of which are characterised by the asymmetrically distributed cartilage lesions.¹⁶. In patients with periosteal chondromas, the chondroma is localised to the bone because it is possible that the tumour will erode the underlying bone resulting in a dip of the bone (saucer-shaped depression). On the side of the tumour that faces the bone, sclerosis forms.¹⁷ 

Systemic effects on bone health

STCs are extra-skeletal, often showing no association with the bone. However, patients with STCs tend to develop non-bone related disorders, often in the tendon, from where they originate, or the surrounding tissues. Generally, STCs are painless, unless they collide with the surrounding structures. Trigger finger is a disorder affecting one or more tendons in the hand making it difficult to bend the thumb and fingers. In rare cases, STCs clinically manifest into trigger finger.¹⁸

Management and treatment of chondromas

Monitoring and observation

Typically, enchondromas and periosteal chondromas do not cause pain, and patients are often asymptomatic. So, they are often diagnosed incidentally by X-rays. Enchondromas appear as small, darkened tumours in the centre of the bone, often containing white spots (of calcification). Periosteal chondromas present on the outside border of the bone and show up as soft tissue. However, STCs do not always show up on X-ray scans because they do not calcify. CT or MRI scans can also be used to diagnose and monitor patients. To diagnose enchondromas, bone scans can also be ordered, where a small dose of radioactive dye is injected which is only taken up by benign and malignant tumours. Alternatively, biopsies could be done on chondromas if the imaging tests are inconclusive. Unfortunately, in the case of enchondroma, biopsies are less reliable because it is difficult to distinguish between a benign enchondroma and a low-grade chondrosarcoma.

Surgical interventions

In most situations, enchondromas do not need treatment, but require consistent monitoring and observation. However, if multiple tumours are present, treatment will be required to avoid weakening of the bone leading to fracture. In such cases, the tumour could be surgically removed by a procedure called curettage, where the tumour is scraped out of the bone. After curettage, the bone cavity may be filled with a bone graft, stabilising the bone. Periosteal and soft tissue chondromas can both be surgically removed and are quickly recognised as distinct, separate masses. Excision surgery, which involves making a skin incision and then removing the tumour entirely, is used to completely remove the tumour. Once completely removed, the tumour rarely returns.

Radiation therapy

Chemotherapy and radiation play a limited role in the treatment of chondrosarcomas.

Summary

Chondromas are benign, slow-progressing tumours that are generally painless. However, in some cases, chondromas can undergo a malignant transformation which may result in severe side effects to the bone including bone erosion, followed by fracture. Often, it is difficult to detect chondroma as patients do not display symptoms, but in some patients, chondromas may be characterised by lumps in the regions they are growing. Benign chondromas are usually left untreated unless they have the potential to develop into malignant chondrosarcomas, in which case they are surgically removed.